A. Why One Side Coating?
This invention is directed to a method for the continuous production of one-side coating of a metallic strand. More particularly, though not limiting in its application, the preferred invention is directed to one-side galvanizing of a ferrous base strip.
Armed with the knowledge of years of experience on the manufacture and use of two-side metallic coated steels, such as galvanized, aluminized, and several proprietary aluminum-zinc coatings, and recent and costly attempts to produce a suitable metallic coating on only one side of a ferrous strand, one may logically ask why sacrifice corrosion protection of one side, especially at a premium cost? The answer is simple--one must respond and be prepared to meet the demands of the consumer/customer. Specifically the automotive industry, spurred by the public for more corrosion resistant car bodies, demanded it. The automakers wanted steels for auto bodies that could offer corrosion resistance to the underside while providing the outside with a suitable surface having the uniformity and paintability of cold-rolled steel strip. It has long been recognized that even special treated galvanized (two-side coating) did not offer a suitable surface for painting. Hence, the answer was one-side galvanized steel strip. Though the answer was simple, the means to achieve the end were not.
Inasmuch as the preferred invention herein deals with continuous hot-dip galvanizing, or at least certain aspects thereof, it may be helpful to review some general characteristics of a galvanizing process.